Corrugated board and corrugated boxes are widely used and well-known. Corrugated boxes are typically assembled from corrugated blanks which are cut from a web of corrugated board. A typical blank is provided with flaps and score lines which are used to assemble the blank into a finished box.
The flaps on a corrugated blank are formed in a machine generally known as a flexo folder gluer, or "flexo" for short. A flexo is exemplary of a machine which has a plurality of rotating tools mounted on a common shaft. A flexo forms the flaps on a blank with a mechanism referred to as a slot-crease-slot mechanism. In a slot-crease-slot, a set of slotting tools is mounted to a first arbor to cut slots in the forward edge of the blank, a set of creasing (scoring) tools is mounted to a second arbor to form fold lines, and a second set of slotting tools is mounted to a third arbor to cut slots in the trailing edge of the blank. This arrangement allows the radial registration of slot location to be done automatically, for example, as shown in U.S. Pat. No. 4,003,300.
Conventional slotting heads on a printer slotter comprise a male tool and a female tool. The male tool is provided with at least one slotter blade which projects beyond the periphery of the tool. The blade is adapted to cooperate with an annular groove in an opposing female slotting tool. The slotting tools are mounted on rotatable parallel shafts.
An inherent manufacturing problem exists in the manufacture of corrugated board done in this manner. Corrugated board by nature is cushioned since it contains air. In order to slot effectively, the air must be removed from the product. This is handled well by the second set of slotting tools since the preceding creasing tools plastically deform the corrugated board prior to slotting, thus removing the air.
The first set of slotting tools does not have any preceding creasing mechanism and must remove the air instantaneously and coincidentally with the commencement of slotting. This results in jagged slots (not sheared but torn instead) and can damage the area at the root of the slot by spalling and fracturing the liners of the board. Corrugated board requires structural strength to allow stacking, and large stresses are concentrated in the corners. Damage to the flaps produces a pre-shear and/or stress riser in the corners which is undesirable, as it causes the product to fail in use.